The present invention concerns a device to produce ice-cream for ice-cream producing machines.
The present invention is applied to ice-cream producing machines of a domestic or semi-professional type.
Machines of a domestic or semi-professional type are known, wherein the container where the ice-cream is formed cooperates with a mixing blade and with means to transfer the cold, or heat absorption means.
The mixing blade takes motion from drive means associated with the cover.
According to a variant, the blade takes motion from drive means located under or at the side of the container and connected to the mixing blade by a drive shaft which passes axially to the container with a cylindrical design. The drive means can be electric or manually driven.
This type of machine, in relation to the chain of cold, has developed different design philosophies in relation to the cooperation of the heat absorption means with the container of the products which are transformed into ice-cream.
A first design philosophy provides a fixed evaporator coil, that is, a coil wherein the temperature of the compressed gas goes down as it expands, which is cylindrical in shape; this coil surrounds the container, leaving an interspace between the coil and the container for the operations to insert and remove the container itself.
This type of solution does not achieve an optimum heat exchange between the coil and the container, given the ring of air which, in fact, is greatly insulating.
To improve the transfer of cold, it was then provided to fill, on each occasion, the ring of air with alcohol or other liquid which does not freeze at the normal working temperatures of the machine.
Apart from the ever-present danger of fire, it is certainly not easy or simple to insert the container into a bath of alcohol. Moreover, there is always the danger of overflow.
A second design philosophy has conceived of an elastic evaporator coil equipped with clamping means, as shown for example in U.S. Pat. No. 4,573,329 and in EP-A-129.706. By acting on the clamping means the evaporator coil opens or closes radially, so that it is possible to insert (or remove) the container by extracting it axially from the coil. When the container is inserted into the evaporator coil, the clamping means are activated and the evaporator coil contracts radially, surrounding, and closely connecting with, the peripheral cylindrical body of the container.
This system guarantees an optimum heat absorption, but it has the drawbacks of the high cost of the evaporator coil and of the fact that it is easily damaged even by a careful user, and even more so by an inattentive user.
Damage to the coil can also entail a dispersion into the environment of dangerous refrigeration gases.
A system is also known, from JP-A-02-145153, which provides that the container is pressed elastically against the rotating mixing blade, by a coil located below.
A proposal is also known, from U.S. Pat. No. 4,535,604, wherein it is provided that the container is held elastically pressed downwards by upper spring means, so that the lower flat part, which connects with the vertical cylindrical part, is in contact with a copper plate, of limited thickness and deformable.
The copper plate is in contact with the coil of cylindrical tubes which involves both the flat part and also the part that connects to the vertical cylindrical part of the container.
This solution is very interesting and advantageous, but it does include some disadvantages. First of all the heat exchange from the plate to the cooled tubes is limited, given the limited contact. Moreover, the presence of the spring located above creates problems of cleaning and safety for the user.
Furthermore, the presence of circumferential blades, necessary to provide the container with the necessary pressure, located laterally or in the upper part of the container, creates not only difficulties in use, but also danger for the user. To this it must be added that, due to its very nature, the elastic mass located under the coil tends to memorize the deformation, and this memorization is accentuated over time. This automatically entails a loss of adherence.
Furthermore, with the system disclosed by US ""604 it is possible to apply pressures of only a few kilograms on the pressure blades, which is not sufficient for a correct contact of heat transmission.
Applicant therefore set himself the problem of finding an optimum solution to these problems and surprisingly found, and also studied, experimented and embodied the present invention.
The present invention is set forth and characterized in the main claim, while the dependent claims describe other innovative characteristics of the invention.
The purpose of the present invention is therefore to improve the performance in the cold chain in correspondence with the heat exchange between the evaporator coil and the container, at the same time achieving an optimum evaporator coil. The invention therefore tends to overcome known problems by achieving a very simple, low cost device, easy to use, simple to clean, without dangers for the user, which is advantageous even for a poorly qualified operator, simple and quick to maintain with little probability of damage.
According to the invention, the system to absorb the heat between the container and the evaporator coil is achieved according to the general principles of US ""604 but with new and innovative concepts.
According to the invention, the coil cooperates with spring means that, in a preferential embodiment, are arranged below a supporting base for the coil. The spring means are able to supply, in their entirety, from 200 to 600 kilograms of total thrust on containers having a diameter of about 130÷160 mm.
The container, when the cover is on, assumes a working position wherein it is thrust elastically against the coil, thanks to the presence of the spring means.
In an advantageous embodiment, the supporting base of the coil is made of plastic.
According to a variant, the cold is transferred through a circular element, for example a toric ring, which affects the bottom of the container.
According to another variant, the circular element also affects the peripheral edge of the container.
The invention provides that the bottom of the container is substantially plane and made of the same material as the rest of the container.
According to a variant, the bottom of the container has a layer of highly conductive material (copper, aluminum or suchlike) the function of which is not only to improve the heat exchange but also to make it uniform.
According to another variant, at least the outer bottom of the container has a series of rings, which cooperate with mating rings present in the evaporator coil, in order to increase the exchange surface.
In this case, one solution provides that the rings are obtained in an additional material applied on the bottom of the container.
The rings can be V-shaped, wavy, or of any other type; only the fact that they serve to increase the exchange surface is relevant.
According to another variant, the bottom of the container is arc-shaped, or like an inner or outer V, or according to another development tending to increase the surface of contact.
According to another variant, the connecting edge between the bottom of the container and the vertical wall of the container cooperates with the evaporator coil.
According to a variant, the coil is a tube with a thickness of between 0.2 and 0.6 mm. The supporting base has a smooth supporting surface for the coil; according to a variant, the supporting surface is shaped in the shape of the coil.
According to a variant, once the coil is positioned, it is subjected to heading which generates at least a substantially plane contact surface on the upper part of the coil, thus improving the support. Advantageously, the heading generates two contact surfaces, one on the upper part and one on the lower part of the coil.
According to the invention, one contact surface is obtained by reducing the height by a value of between 5% and 20%.
According to one embodiment of the invention, between the container and the coil there is an intermediate plate, made of copper or aluminum, or iron, or plastic material; obviously, the terms copper, aluminum and iron also include the relative alloys.
The thickness of the intermediate plate is between 0.1 and 0.6 mm, also depending on the material used to make it.
According to the invention, the mixing blade not only performs the known function of mixing and introducing air into the ice-cream, but also the function of continuously raising the material, so that the cold transmitted to the bottom of the container and, from this, to the material in contact, is continuously carried upwards with a progressive uniformization of the temperature in the product. According to a variant, the mixing blade is shaped so as to cooperate in close proximity with the bottom of the ice-cream container.
Applicant has also found that the size of the container, that is, the ratio between the usable inner diameter and the height of the level of product which can be obtained (that is, the ice-cream) improves the performance of the device according to the invention.
According to a variant of the invention, this ratio is between 0.30 and 0.50, advantageously between 0.38 and 0.42.
According to the invention, also considering that domestic or semi-professional ice-cream producing machines suffer from natural vibrations, the contact between the intermediate plate with the container and the evaporator coil must always be kept constant and this constant contact is maintained by a conductive paste or other suitable plastic material, located in cooperation with the coil.
According to the invention, the contact between the container and the plate-coil system is maintained elastically due to the elastic thrust towards the container of the evaporator coil while the container remains fixed, in the working phase.
According to the invention, the evaporator coil deforms elastically according to the thrust that it receives towards the container; this improves the heat yield.
According to another variant, the coil is incorporated into a melted material, such as copper, aluminum or suchlike, or into said conductive paste, in order to improve the distribution and uniformity of the cold.